In diffusion transfer photography using a "peel apart" photographic material, a light-sensitive element typically is exposed, superposed with an image-receiving element and developed to transfer a silver or dye image from the light-sensitive element to the image-receiving element, after which the two elements are peeled apart to produce a photographic containing the transferred image, for example, as disclosed in U.S. Pat. No. 2,983,606 and K. I. Jacobson and R. E. Jacobson, Imaging Systems, pages 91-102, The Focal Press, London (1976). The quality of the image formed on the image receiving element, largely depends upon the hygroscopicity of the light-sensitive element and the image receiving element, and the degree of swelling of each element must be controlled during development to provide sufficient image density and to avoid density mottle in the formed image. In addition, if the layer of developing solution inserted between the superposed elements is too thick, a sufficiently sharp image cannot be formed, and if the layer is too thin, sufficient image density cannot be attained and some density mottle occurs, and further, white spots often appear in the image due to air-bubbles present on the image forming surface.
British Pat. No. 1,533,924 discloses a peelapart material containing a hygroscopic layer, whereby the distance between the light-sensitive element and the image receiving element may be reduced, after the hygroscopic layer is swollen, and thus, the sharpness of the formed image may be increased. Such conventional materials have the disadvantage, however, that sufficient image density cannot be attained, and some density mottle occurs.